1. Field of the Invention
The present invention relates to an angular rate sensor used for controlling the motion of a vehicle and an aircraft.
2. Description of Related Art
FIG. 19 is a top view showing a conventional angular rate sensor disclosed in U.S. Pat. No. 5,408,877. FIG. 20 is a sectional view along the line XXxe2x80x94XX of FIG. 19. In these figures, the reference numeral 101 designates an inertial mass; 102 designates a drive gimbal frame on which the inertial mass is mounted; 103 designates a detection gimbal frame surrounding the drive gimbal frame 102; 104 designates a first torsion beam connecting the drive gimbal frame 102 with the detection gimbal frame 103 to rotatably support the drive gimbal frame 102 at two opposed positions; 105 designates a second torsion beam rotatably supporting the detection gimbal frame 103 at two opposed positions; 106 designates a drive electrode disposed below the drive gimbal frame 102 apart from the frame 102 by a certain gap; 107 designates a detection electrode disposed above the detection gimbal frame 103; and 108 designates a silicon substrate supporting the second torsion beam 105 and the drive electrodes 106.
The torsion axes of the first torsion beams 104 are parallel to the Y axis, while the torsion axes of the second torsion beams 105 are parallel to the X axis. The torsion axes of the first torsion beams 104 are perpendicular to the torsion axes of the second torsion beams 105.
The drive electrodes 106 are parallel to the torsion axes of the first torsion beams 104. These two electrodes 106 are symmetrically placed about the line extended from the torsion axes of the first torsion beams 104 viewed from the direction of the Z axis.
The detection electrodes 107 parallel to the torsion axes of the second torsion beam 105 are symmetrically placed about the line extended from the torsion axes of the second torsion beams 105 viewed from the direction of the Z axis.
Next, the operation of the conventional angular rate sensor will be described.
On applying alternating voltages with mutual phase-difference of 180 degrees to the two drive electrodes 106, an electrostatic attractive force induced between the drive gimbal frame 102 and one of the drive electrodes 106 leads to torsion of the first torsion beams 104, causing a rotational oscillation of the drive gimbal frame 102 (reference oscillation) about the torsion axes of the first torsion beams 104 which function as a rotational axis. As a result, the mass center of the inertial mass 101 oscillates in a simple harmonic motion in the direction parallel to the X axis.
In this state, the rotation of the entire angular rate sensor about the Z axis generates the Coriolis force represented by the following equation (1) acting on the center of the inertial mass 101 in the direction parallel to the Y axis. The second torsion beams 105 are then distorted and the detection gimbal frame 103 rotationally oscillates about the torsion axes of the second torsion beams 105 as a rotational axis.
F=2VMxcexa9xe2x80x83xe2x80x83(1)
wherein V represents a rate of the inertial mass 101 in the direction parallel to the X axis, M represents an inertial mass and xcexa9 represents a rotational angular rate about the Z axis.
The displacement amplitude of the rotational oscillation of the detection gimbal frame 103 is proportional to the maximum absolute value of the Coriolis force F which is proportional to the angular rate xcexa9. Further, as the detection gimbal frame 103 rotationally oscillates, the electrostatic capacity between the detection gimbal frame 103 and the detection electrode 107 changes. This change in electrostatic capacity is converted into a voltage to obtain a sensor output proportional to the angular rate xcexa9.
As stated above, in the conventional angular rate sensor the electrostatic attractive force generated between the drive gimbal frame 102 and the drive electrodes 106 is used for inducing reference oscillation. The electrostatic attractive force is inversely proportional to the square of the distance between the drive gimbal frame 102 and the drive electrodes 106. Thus, once the first torsion beams 104 are greatly distorted, the rotational angle of the drive gimbal frame 102 increases and the distance between the drive gimbal frame 102 and one of the drive electrodes 106 decreases. As a result, an electrostatic attractive force exceeds the restoring force of the first torsion beams 104, causing the Pulled-in phenomenon where the drive gimbal frame 102 is attached to one of the drive electrodes 106. Consequently, the displacement amplitude of the rotational oscillation of the drive gimbal frame 102 is limited such that the distance between the drive gimbal frame 102 and the drive electrodes 106 is not more than one third of the gap therebetween for a stable rotational oscillation of the drive gimbal frame 102.
Since the conventional angular rate sensor is constructed as above, the displacement amplitude of the rotational oscillation of the drive gimbal frame 102 is limited for avoiding the Pulled-in phenomenon. As a result, a rate V of the mass center of the inertial mass 101 in the direction parallel to the X axis is limited and the Coriolis force F is thus limited. In other words, there exists a problem that the displacement amplitude of the rotational oscillation of the drive gimbal frame 102 is limited, and hence the sensitivity of the angular rate sensor is limited.
Alternatively, in a case that an angular rate sensor of high sensitivity is designed under the condition that the distance between the drive gimbal frame 102 and the drive electrodes 106 is not more than one third of the gap therebetween, a large gap is required for a large displacement amplitude of the rotational oscillation of the drive gimbal frame 102. However, in this case, since a large electrostatic attractive force is required, larger driving voltages should be applied to the drive electrodes 106 and the facing areas between the drive gimbal frame 102 and the drive electrodes 106 should be larger. This design is impractical.
In addition, there is another problem that the conventional angular rate sensor can detect only a rotational angular rate about one axis.
The present invention is implemented to solve the above problems. An object of the present invention is to provide an angular rate sensor of high sensitivity with a drive frame and a frame to be driven (hereinafter referred to as driven frame) separately provided, in which the driven frame is not directly but indirectly driven through the drive frame.
Another object of the present invention is to provide an angular rate sensor capable of detecting rotational angular rates about a plurality of axes.
According to a first aspect of the present invention, there is provided an angular rate sensor comprising: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions; driven frame torsion beams rotatably supporting the driven frame at two opposed positions; a drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams; driving force generation means for giving a driving force to cause a bending oscillation of the drive frame in an out-of-plane direction; link beams connecting the driven frame with the drive frame; and detection means for detecting a displacement amplitude of a rotational oscillation of the inertial mass.
According to a second aspect of the present invention, there is provided an angular rate sensor comprising: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions; driven frame torsion beams rotatably supporting the driven frame at two opposed positions; a drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams to support the driven frame torsion beams; driving force generation means for giving a driving force to cause a bending oscillation of the drive frame in an out-of-plane direction; and detection means for detecting a displacement amplitude of a rotational oscillation of the inertial mass; wherein a center of gravity of the driven frame is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame.
Here, the angular rate sensor may further comprise monitor means for monitoring a displacement amplitude of a rotational oscillation of the driven frame.
A mass center of the inertial mass may be positioned on a line extended from torsion axes of the driven frame torsion beams or shifted from the line, viewed from the direction perpendicular to top and bottom surfaces of the driven frame. The driven frame rotationally oscillates about the torsion axes of the driven frame torsion beams or another axis as a rotational axis. It often rotationally oscillates about an axis between the torsion axes of the driven frame torsion beams and longitudinal axes of the link beams.
A mass center of the inertial mass may be positioned on a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame; and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces thereof: and torsion axes of the inertial mass torsion beams may be perpendicular to the torsion axes of the driven frame torsion beams.
A mass center of the inertial mass may be shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame; and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces thereof: and torsion axes of the inertial mass torsion beams may be perpendicular to the torsion axes of the driven frame torsion beams.
A mass center of the inertial mass may be shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame; and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces thereof: and torsion axes of the inertial mass torsion beams may be parallel to the torsion axes of the driven frame torsion beams.
The link beams may be connected to the driven frame near the driven frame torsion beams.
The inertial mass and the inertial mass torsion beams may be at least two of; a first inertial mass whose mass center is positioned on a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and first inertial mass torsion beams connecting the first inertial mass with the driven frame, torsion axes of the first inertial mass torsion beams being perpendicular to the torsion axes of the driven frame torsion beams; a second inertial mass whose mass center is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and second inertial mass torsion beams connecting the second inertial mass with the driven frame, torsion axes of the second inertial mass torsion beams being perpendicular to the torsion axes of the driven frame torsion beams; and a third inertial mass whose mass center is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and third inertial mass torsion beams connecting the third inertial mass with the driven frame, torsion axes of the third inertial mass torsion beams being parallel to the torsion axes of the driven frame torsion beams: and the angular rate sensor may comprise at least two rotational angular rate detection parts of; a first rotational angular rate detection part having the first inertial mass and the first inertial mass torsion beams; a second rotational angular rate detection part having the second inertial mass and the second inertial mass torsion beams; and a third rotational angular rate detection part having the third inertial mass and the third inertial mass torsion beams.
The inertial mass may be first and second inertial masses whose mass centers are symmetrically placed about a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and the inertial mass torsion beams may be first inertial mass torsion beams connecting the first inertial mass with the driven frame and second inertial mass torsion beams connecting the second inertial mass with the driven frame, torsion axes of the first and second inertial mass torsion beams being parallel to each other.
The drive frame may be a first drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams and a second drive frame surrounding the other half circumference of the driven frame.
The driving force generation means may comprise a piezoelectric element provided on the drive frame, an electrode provided below the drive frame or a piezoresistor formed in the drive frame.
The detection means may comprise piezoresistors formed in the inertial mass torsion beams or an electrode provided below the driven frame.
The monitor means may comprise a piezoelectric element provided on the drive frame, an electrode below the drive frame or piezoresistors formed in the driven frame torsion beams.
As stated above, according to an aspect of the present invention, an angular rate sensor is constructed to comprise: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions; driven frame torsion beams rotatably supporting the driven frame at two opposed positions; a drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams; driving force generation means for giving a driving force to cause a bending oscillation of the drive frame in an out-of-plane direction; link beams connecting the driven frame with the drive frame; and detection means for detecting a displacement amplitude of a rotational oscillation of the inertial mass. Consequently, there can be advantageously provided the angular rate sensor whose sensitivity is high, since the displacement amplitude of the rotational oscillation of the driven frame is not limited.
According to an aspect of the present invention, an angular rate sensor is constructed to comprise: an inertial mass; a driven frame surrounding the inertial mass; inertial mass torsion beams connecting the inertial mass with the driven frame to rotatably support the inertial mass at two opposed positions; driven frame torsion beams rotatably supporting the driven frame at two opposed positions; a drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams to support the driven frame torsion beams; driving force generation means for giving a driving force to cause a bending oscillation of the drive frame in an out-of-plane direction; and detection means for detecting a displacement amplitude of a rotational oscillation of the inertial mass; wherein a center of gravity of the driven frame is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame. Consequently, there can be advantageously provided the angular rate sensor where the driven frame can rotationally oscillates in simple construction, since when the bending oscillation of the drive frame is transmitted to the entire driven frame through the driven frame torsion beams, a drive inertial force acts on the driven frame to cause the rotational oscillation of the driven frame about the torsion axes of the driven frame torsion beams as a rotational axis.
According to an aspect of the present invention, an angular rate sensor is constructed to further comprise monitor means for monitoring a displacement amplitude of a rotational oscillation of the driven frame. Consequently, there can be advantageously provided the angular rate sensor where the displacement amplitude of the rotational oscillation of the driven frame can be maintained constant by maintaining the output voltage from the monitor piezoelectric element constant.
According to an aspect of the present invention, an angular rate sensor is constructed such that the link beams are connected to the driven frame near the driven frame torsion beams. Consequently, there can be advantageously provided the angular rate sensor which can be driven at a low voltage, since even if the displacement amplitude of the bending oscillation of the drive frame is small, the displacement amplitude of the rotational oscillation of the driven frame is large.
According to an aspect of the present invention, an angular rate sensor is constructed such that the inertial mass and the inertial mass torsion beams are at least two of; a first inertial mass whose mass center is positioned on a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and first inertial mass torsion beams connecting the first inertial mass with the driven frame, torsion axes of the first inertial mass torsion beams being perpendicular to the torsion axes of the driven frame torsion beams; a second inertial mass whose mass center is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and second inertial mass torsion beams connecting the second inertial mass with the driven frame, torsion axes of the second inertial mass torsion beams being perpendicular to the torsion axes of the driven frame torsion beams; and a third inertial mass whose mass center is shifted from a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and third inertial mass torsion beams connecting the third inertial mass with the driven frame, torsion axes of the third inertial mass torsion beams being parallel to the torsion axes of the driven frame torsion beams: and the angular rate sensor comprises at least two rotational angular rate detection parts of; a first rotational angular rate detection part having the first inertial mass and the first inertial mass torsion beams; a second rotational angular rate detection part having the second inertial mass and the second inertial mass torsion beams; and a third rotational angular rate detection part having the third inertial mass and the third inertial mass torsion beams. Consequently, there can be advantageously provided the angular rate sensor capable of detecting rotational angular rate about two or more axes.
According to an aspect of the present invention, an angular rate sensor is constructed such that the inertial mass is first and second inertial masses whose mass centers are symmetrically placed about a line extended from torsion axes of the driven frame torsion beams, viewed from the direction perpendicular to top and bottom surfaces of the driven frame, and positioned above the top surface of the driven frame or below the bottom surface thereof, viewed from the direction parallel to the top and bottom surfaces of the driven frame; and the inertial mass torsion beams are first inertial mass torsion beams connecting the first inertial mass with the driven frame and second inertial mass torsion beams connecting the second inertial mass with the driven frame, torsion axes of the first and second inertial mass torsion beams being parallel to each other. Consequently, there can be advantageously provided the angular rate sensor which can detect an angular rate with high sensitivity, since in a state that the driven frame rotationally oscillates, when the entire angular rate sensor rotates about an axis parallel to the torsion axes of the first and second inertial mass torsion beams, the first and second inertial masses rotationally oscillate in phases different from each other by 180 degrees.
According to an aspect of the present invention, an angular rate sensor is constructed such that the drive frame is a first drive frame surrounding a half circumference of the driven frame referenced to a line extended from torsion axes of the driven frame torsion beams and a second drive frame surrounding the other half circumference of the driven frame. Consequently, there can be advantageously provided the angular rate sensor which can detect an angular rate with high accuracy, since the driven frame stably rotationally oscillates.
According to an aspect of the present invention, an angular rate sensor is constructed such that the driving force generation means comprises a piezoelectric element provided on the drive frame. Consequently, there can be advantageously provided the angular rate sensor which can be driven at a low voltage, since a driving force can be supplied to the drive frame at a low voltage to cause a bending oscillation of the drive frame.